Among the oxide superconducting wire, YBa2Cu3O7-x (YBCO) superconducting wire has the structure that a biaxially-oriented thin film of one layer or plural layers comprising the inorganic material is formed onto the metallic substrate, and that the superconducting film and the stabilized layer are formed in sequence onto the biaxially-oriented thin film of the inorganic material. Because this wire has the biaxially-oriented crystal, the critical current (Ic) value is higher than the bismuth type silver sheathed wire, and the magnetic-field property is superior in the liquid nitrogen temperature. Therefore, by using this wire, it is expected that the superconducting equipment which is used in the low temperature at present can be used in the high temperature state.
The characteristic of this YBCO superconductor is affected strongly by the orientation of that crystal. Therefore, the characteristic of this YBCO superconductor is affected strongly by this substrate which constitutes the lower layer and by the orientation of the crystal of the intermediate layer.
That is, a crystal system of the YBCO superconductor is an orthorhombic crystal. Therefore, in order to bring out the characteristic of the material in conducting property, it is required that not only a CuO face of the crystal but also an in-plane crystal orientation is aligned. The reason is that because a little mismatch of the orientation generates grain boundaries of the twin crystal, the conducting property deteriorates.
Various methods are studied now for the film formation of the YBCO superconducting wire. IBAD (Ion Beam Assisted Deposition) method or RABiTS (Trade Mark: Rolling Assisted Biaxially Textured Substrate) method is known as the manufacturing technology of the biaxially-oriented metal substrate that the in-plane oriented intermediate layer is formed onto the tape-shaped metal substrate. And many YBCO superconducting wires are reported. These YBCO superconducting wires have the intermediate layer whose in-plane orientation degree and orientation are improved, and the intermediate layer is formed onto non-oriented or oriented metal tape. For example, the following rare earth-containing tape-shaped oxide superconductor is known. As the substrate, that rare earth type tape-shaped oxide superconductor uses the substrate which consists of Ni or Ni based alloy having oriented texture by heat treatment after strong rolling process. And the oxide intermediate layer of the thin film of Ni oxide, CeO2 and so on which is formed by MOD method and the YBCO superconducting layer are formed in sequence onto the surface of this substrate. (for example, refer to Patent document No. 1).
Among the background arts, the method using IBAD substrate has the highest characteristic. The superconducting wire by this method is formed by using following steps. Onto the tape-shaped Ni based substrate (hastelloy and so on) having nonmagnetism and high strength, the intermediate layer (CeO2, Y2O3, YSZ and so on) or the intermediate layer having two layer structure (YSZ or Gd2Zr3O7/CeO2 or Y2O3 and so on) is formed by depositing the particles generated from the target using laser evaporation during irradiation of ion from the diagonal direction for this Ni based substrate. These intermediate layers have high orientation and inhibits the reaction with the elements which constitute the superconductor. And after forming the CeO2 film onto that layer by PLD method, the YBCO layer is formed by PLD method (for example, refer to Patent document No. 2).
However, in this method, because all layers are formed by vacuum process of gas phase method, there is advantage that the dense and smooth intermediate layer film can be obtained. But there are problems that the film formation speed is slow, the equipment cost becomes high and the wire cost rises. Although some film formation methods have been studied other than this IBAD method, the available methods for solving about the problems of the cost and the formation speed have not been reported.
Chemical vapor deposition method (CVD) has the problem that although manufacturing speed is fast than other vapor phase methods, it is difficult to increase the film thickness for obtaining high Ic value. The most effective method to actualize the low cost is MOD method (Metal Organic Deposition Processes) which forms the oxide layer by using the metal organic acid salt or the organic metallic compound as the raw material, and by giving the heat treatment after coating the raw material.
Because this process does not use the vacuum process, there are advantages that the equipment cost and the maintenance cost are low. Therefore, it is expected that this process provides the low cost superconductor. In this case, if the film of the intermediate layer also can be formed by MOD process, it is possible to decrease the cost furthermore.
The important point in the film formation process of the YBCO superconducting layer by this MOD process is the atmosphere control at the time of baking. Especially, it is that the baking process is established so that the uniform gas flow can be sprayed on the surface of the calcination film.
Heretofore, for the purpose of forming the stable atmosphere in the axial direction of the tubular furnace, the atmosphere control type furnace for heat treatment which has the following structures is known. That is, the tube of furnace-core is double structure. And two pairs of gas-supplying-channels and gas-discharging-channels are formed by arranging the four partition boards between the outer tube and the inner tube. Besides, the plural gas-outflow-holes in gas-supplying-channels and the plural gas-inflow-holes in gas-discharging-channels are arranged (for example, refer to Patent document No. 3).    Patent document No. 1: Japanese Patent Publication No. 2004-171841    Patent document No. 2: Japanese Patent Publication No. Hei04-329867    Patent document No. 3; Japanese Patent Publication No. 2003-121076